This invention relates to the in-situ combustion of hydrocarbons in a subsurface formation and more particularly, to an improved well completion which permits the safe injection of high purity oxygen into a well.
In-situ combustion for the recovery of hydrocarbons from subsurface formations is becoming increasingly prevalent. Combustion is initiated in the subsurface formation and the resulting combustion zone moves through the formation by the injection of air or oxygen. By carefully controlling the injection of oxygen and water into the formation, the combustion zone progresses in a manner which facilitates the recovery of hydrocarbons from the formations. U.S. Pat. Nos. 3,240,270--Marx, 4,031,956--Terry, and 4,042,026--Pusch, et al are examples of the recovery of hydrocarbons by in-situ combustion.
In such processes, the prevention of unintended ignition is of primary concern. For example, as the combustion zone expands away from the injection well, a large volume of unreacted oxygen sometimes accumulates near the well. If this travels upwardly in the well, a catastrophic fire possibly destroying the well, can be ignited. U.S. Pat. No. 3,135,324--Marx discusses the ignition problem.
The use of oxygen in such fire flooding processing has been limited because of the stringent requirement that the oxygen be supplied through a clean pipe. Contamination which is normally found in well tubing strings is a severe fire hazard in the presence of oxygen. A typical oxygen driven fire flood operation alternately supplies water and oxygen through the same tubing string to the formation. Coatings which are normally applied to tubing strings which convey water cannot be used because they react with the oxygen. On the other hand, using stainless steel tubing strings of sufficient diameter to conduct water would be prohibitively expensive.
It is an object of the present invention to provide a well completion which can be safely used in an oxygen driven fire flooding process.
It is a further object of the present invention to provide a fire flooding process which can be conventionally ignited with air and, thereafter, converted to an oxygen driven fire flood.